In general, a mobile communication system was developed to provide a voice service while guaranteeing activity of users. However, the mobile communication system has gradually expanded a service area thereof from the voice service to a data service. In recent years, the mobile communication system has been developed to the extent that a high-speed data service can be provided. However, since there are a resource shortage phenomenon and a demand for a higher speed service by users in the current mobile communication system providing services, a more-advanced mobile communication system is needed.
To meet the demand, standardization of Long Term Evolution (LTE) is being progressed by 3rd Generation Partnership Project (3GPP) as one of next generation mobile communication systems which are being developed. LTE is a technology for implementing high speed packet based communication having a transmission rate of a maximum of 100 Mbps. For the transmission rate, various plans are being discussed. For example, there are plans to reduce the number of nodes located on a communication path through a simple network structure and to bring wireless protocols as close as possible to a wireless channel.
In such a mobile communication system, a User Equipment can use a plurality of heterogeneous networks at the same time. Specifically, the User Equipment can use a 3GPP access network, such as a GERAN, an UTRAN, or an E-UTRAN, and a non-3GPP access network, such as a WLAN, at the same time. For example, a User Equipment can access an E-UTRAN and transmit/receive data, and simultaneously, can access a WLAN for other traffic and transmit/receive data. For such simultaneous accesses to heterogeneous networks, a method for exchanging parameters between a User Equipment and the networks, and a method for controlling QoS are required.